The present invention relates to sunglass lenses, in particular sunglass lenses with refractive power.
It is known in the prior art to manufacture non-corrective eyeglasses such as sunglasses or protective eyeglasses having wrap-around segments designed to shield the eye from incident light, wind, and foreign objects in the temporal vision field of the wearer.
Visible light and light in the UV region may enter the eye from angles as high as 100xc2x0 from the line of sight.
It has not been possible, however, in prior art sunglasses or protective eyeglasses, to provide spectacle lenses with refractive power. The radii of curvature required to provide an ophthalmic lens defining a prescription zone is such that the spectacles would produce a bug-eyed appearance, which would be cosmetically unacceptable.
Whilst attempts have been made in the prior art to provide a wrap-around sun shield over otherwise generally standard prescription eyeglasses, such products are generally cosmetically unacceptable and suffer from significant optical distortions.
It is accordingly an object of the present invention to overcome, or at least alleviate, one or more of the difficulties and deficiencies related to the prior art.
Accordingly, in a first aspect, there is provided an optical lens element including
a front and back surface capable of forming a prescription (Rx) zone; and
a peripheral temporal zone.
Applicants have discovered that it is possible to provide a sufficient area of the lens to function as a prescription zone and yet still to provide a lens which provides a shield in the area of the temples. This is achieved by having a peripheral temporal zone.
By the term xe2x80x9coptical lens elementxe2x80x9d as used herein, we mean an optical or ophthalmic lens, semi-finished lens or lens formed from a pair of lens wafers which may be utilised in the formation of an optical lens product.
The ophthalmic lens element may be a lens of negative or positive refractive power. Where the ophthalmic lens element includes an ophthalmic lens wafer, the peripheral temporal zone may be provided by the front wafer.
The optical lens element according to the present invention may be adapted for mounting in a frame of the wrap-around or shield type.
The peripheral temporal zone may be at least in part of generally toric shape. The peripheral temporal zone may-be at least in part generally piano.
The peripheral temporal zone may itself form an extension of the prescription zone or may be a non-prescription zone.
In an alternative or additional aspect, the peripheral temporal zone may be modified to permit light control within the zone.
The lens element may be rotated temporally about a vertical axis through the optical centre thereof or the optical axis may be decentred relative to the geometric axis, or the lens element may be both rotated and decentred.
It will be understood that the peripheral temporal zone, for a typical sunglass lens element of the wrap-around type, may for example extend for approximately 10 to 25 mm.
In a further aspect of the present invention, there is provided an optical lens element providing prescription (Rx) correction generally in the range xe2x88x926.0 D to +6.0 D with 0 to +3 cyl
wherein the front surface is capable of being mounted in a frame of constant design curve irrespective of the Rx, such frame curves being 5.0 D and above; and
the back surface provides good clearance from temples or eye lashes.
The ophthalmic lens element may form part of a series of lens elements, e.g. of the type described in International Patent Application PCTIEP97/00105, the entire disclosure of which is incorporated herein by reference.
Preferably the front surface is capable of being mounted in a frame of constant design curve of between 8.0 D and 9.0 D.
More preferably the front surface of the lens element has a high curve extending from nasal to temporal limits, but the vertical curve is 6.0 D or below.
It will be understood that such vertical curves permit the final prescription lenses, preferably edged lenses, to be adapted to the shape of the wearer""s face and so locate closely in a form of the wrap-around type (so-called xe2x80x9ctoricxe2x80x9d design).
Alternatively the optical lens elements may be adapted for mounting in a frame of the shield type. Accordingly in a still further aspect of the present invention there is provided a unitary optical lens including
a pair of optical lens elements, each lens element providing prescription (Rx) correction generally in the range xe2x88x926.0 D to +6.0 D with 0 to +3 cyl
wherein the front surface is capable of being mounted in a frame of constant design curve irrespective of the Rx, such frame curves being 5.0 D and above; and
the back surface provides good clearance from temples or eye lashes.
Accordingly in a particularly preferred embodiment the present invention provides a spectacle frame, or a unitary lens, including a pair of optical lens elements, which lens elements provide true Rx correction in a prescription (Rx) zone for a wearer up to 50xc2x0 off axis, preferably 80xc2x0 off axis, and terminating in a peripheral temporal zone, that provides clear perception of objects in the peripheral area of human vision and avoids prismatic jump from the prescription zone to the peripheral temporal zone.
The optical lens element according to the present invention may, when mounted, in a spectacle frame, be rotated temporally about a vertical axis through the optical centre thereof.
Accordingly in a further aspect of the present invention, there is provided an optical lens element adapted for mounting in a frame of the wrap-around or shield type, such that the lens element is rotated temporally about a vertical axis through the optical centre thereof, the lens element including
a front and back surface capable of forming a prescription (Rx) zone; and optionally
a peripheral temporal zone;
the front and/or back surface bearing a surface correction to at least partially adjust for errors including astigmatic and power errors.
In this embodiment, whilst the optical axis continues to intersect the line of sight of the wearer, a number of optical effects and errors are thus introduced as discussed below. However, by suitable selection of the combination of front and/or back surface, the optical errors may be reduced or eliminated.
Accordingly, in a still further aspect of the present invention there is provided an optical lens element adapted for mounting in a frame of the wrap-around or shield type, the lens element including
a front and back surface capable of forming a prescription (Rx) zone; and optionally
a peripheral temporal zone wherein the optical axis is decentred relative to the geometric axis of the lens element to provide for prismatic correction,
the front and/or back surface bearing a surface correction to at least partially adjust for errors including astigmatic and power errors.
Applicants have discovered that it is possible to produce an optical lens element, preferably a sunglass lens element, which includes a prescription (Rx) zone and which is decentred to provide a prismatic correction.
Preferably the front and/or back surface of the optical lens element further includes a surface correction to at least partially adjust for prismatic errors introduced by lens tilt.
Illustrative optical effects and errors may be summarised as follows:
The effects are described by consideration of the effects seen by the wearer along the line of sight that intersects the optical axis of the lens element:
Astigmatic Error
There is an induced astigmatic error such that the astigmatism, a, is proportional to the power of the lens, P, and proportional to the square of the rotation angle of the lens.
Power Errors
When the lens is used in a wrap-around form the mean through power of the lens changes. The mean power error, dP, is proportional to the astigmatic error, a, and proportional to a constant, k, that is related to the index of the lens. Hence in a minus Rx the mean power becomes more negative and in a plus Rx the mean power becomes more positive.
Prismatic Effects
Due to the rotation of the lens and the oblique angle of the optical axis, lens prism is introduced.
Off-axis Prismatic Disparity
Off-axis prismatic disparity will result from unequal distortions in the temporal and nasal fields, resulting in poor binocular vision.
Other important observations:
The lens element described may result in increased off-axis power and astigmatic errors due to the selection of a base (front) curve that is designed to fit standard wrap frames, rather than for best optical performance.
These errors may result in un-accommodatable power errors.
One or more of the following corrections may be introduced to reduce the errors described:
Mean Power Error Correction
The front and/or back surface curvature may be adjusted to account for the change in mean power resulting from rotation of the lens, the degree of correction depending upon a balance of wearer tolerable on-axis power error and reduction of un-accommodatable off-axis power errors.
Hence a full power correction for the introduced shift in through power to correct on-axis errors may be applied or a partial correction when off-axis power error is considered.
Astigmatic Error Correction
The front and/or back surface may at least in part be toric in nature to correct for astigmatic error resulting from the lens rotation discussed earlier. The degree of correction may fully correct for the astigmatism introduced due to rotation of the lens or may be partially corrected depending upon the application. A partial correction may be applied to achieve a tolerable on-axis astigmatic error so as to reduce the off-axis astigmatic errors.
Prismatic Correction
The optical centre may be shifted horizontally to compensate for prism induced by the lens rotation. This may be achieved by applying prescribed prism during surfacing or shifting of the lens element in a horizontal direction.
Additional Considerations
These corrections include, but are not limited to, pantoscopic lens tilt, variation in lens frame types, cosmetic requirements and average pupil-centre to lens distances depending on frame and lens form types.
Off-axis Prismatic Disparity
To correct for off-axis prismatic disparity the lens may include an aspheric surface on either the front or back surfaces, or both.
Aspherisation of Surfaces
Aspherisation of either the front or back surfaces may be utilised to correct for off-axis errors including errors introduced due to tilt and/or the selection of the base curves. Such off-axis error may include power and astigmatic error and prismatic disparity.
It will be understood, however, that whilst it is relatively simple to correct for any particular optical error, it is necessary to balance the correction to achieve acceptable overall performance of the lens.
Illustrative error corrections which may be undertaken for a typical rotation of approximately 20xc2x0 about the vertical axis, for a range of plus (+) and (xe2x88x92) tens elements of varying power, are given in the following Table.
It is to be noted that the eyeside surface power corrections given assume that the above errors are fully corrected to recover the sphere Rx specified at the optical centre. Lesser corrections may be undertaken, if required, to achieve acceptable overall performance of the lens.
Accordingly in a preferred aspect the optical lens element includes
a front and/or back surface having a surface curvature adjusted to partially compensate for central mean through power error; and
a second surface correction to at least partially balance off-axis and on-axis astigmatic errors.
In a still further preferred aspect, the second surface correction may include a toric component on the front and/or back surface to at least partially correct for astigmatic error.
Lens correction included in the optical lens element of the present invention may be grouped as two types:
those corrections that result from the lens rotation about the optical axis, or astigmatic and power error correction,
and those corrections required by the wearer""s prescription, or prescription correction.
The front surface may, in a preferred aspect, include a base curvature appropriate for high base curve lenses, e.g. for wrap around use. The nature of the front surface may mainly be dictated by cosmetic requirements.
Desirably, the front and/or back surface(s) of the optical lens element includes a spherical or toric component to provide the desired prescription (Rx) in the prescription zone.
More preferably the front and/or back surface includes a toric component and bears a surface correction to at least partially adjust for on-axis astigmatic and mean power errors. Such on-axis errors may result from the temporal rotation of the lens when mounted in a wrap-around or shield type frame.
Alternatively, or in addition, the front and/or back surface includes an aspheric component selected to at least partially adjust for off-axis astigmatic and mean power errors as well as prismatic disparity.
Preferably the front surface includes such an aspheric component. Such off-axis errors may result in part from the temporal rotation of the lens when mounted in a wrap-around or shield type frame and in part from the selection of a base curvature appropriate for high base curve lenses.
In a further preferred aspect, in order to provide the peripheral temporal zone the front and/or back surface, preferably the front surface, is an aspheric surface that includes appropriate aspheric coefficients to define a peripheral temporal zone.
Alternatively, the peripheral temporal zone may be provided by having an extension of the curvature of the front and/or back surface, the opposite surface being modified to complement the extended surface.
Accordingly the optical tens element includes
a front surface including a spherical or toric component designed to provide the desired prescription (Rx) in the prescription zone, and bearing a surface correction to at least partially adjust for errors including astigmatic and mean power errors, in combination with the back surface,
and including appropriate co-efficients to define a peripheral temporal zone; and a transition section therebetween designed to smoothly blend the prescription zone and peripheral temporal zone
a back surface modified to complement the front surface.
Preferably the front surface in the peripheral temporal zone is generally spherical. More preferably the back surface is also generally spherical and of equal curvature to the peripheral temporal zone, thus providing a generally piano extension.
The back surface may preferably include a base curvature such that the patient""s required prescription power, Rx, is achieved. The back surface may be further modified to complement the front surface selected.
The back surface of the ophthalmic lens element according to the present invention may accordingly, in a preferred aspect, include a toric surface selected to achieve the prescribed optical power and the prescribed lens cylinder correction.
In a preferred aspect, the toric back surface may further include a surface correction to compensate for mean power and astigmatic errors introduced by lens wrap.
In a still further preferred aspect, the toric surface may be an aspheric surface. The aspheric toric surface may include an adjustment to correct off-axis astigmatic and/or mean power errors.
Accordingly, in a preferred aspect the optical lens element includes
a spherical front surface that includes a base curvature appropriate for high base curve lenses, and
a toric back surface of appropriate curvature to provide the prescribed optical lens power and prescribed lens cylinder requirement and including an adjustment for astigmatic and mean power errors to compensate for lens wrap.
In an alternative embodiment, the optical lens element includes
a toric front surface that includes a base curvature appropriate for high base curve lenses, and a toric adjustment for astigmatic error correction to compensate for lens wrap, and
a toric back surface of appropriate curvature to provide the prescribed optical lens power and prescribed lens cylinder.
In a further alternative embodiment, the optical lens element includes
an aspheric front surface that includes a base curvature appropriate for high base curve lenses and appropriate aspheric coefficients to correct for off-axis power and/or astigmatism errors; and
a toric back surface of appropriate curvature to provide the prescribed optical lens power and prescribed lens cylinder requirement that includes adjustments for astigmatic error correction to compensate for lens wrap.
In a still further alternative embodiment, the optical lens element includes
an aspheric toric front surface that includes a base curvature appropriate for high base curve lenses, and a toric adjustment for astigmatic error correction to compensate for lens wrap, and
a toric back surface of appropriate curvature to provide the prescribed optical lens power and prescribed lens cylinder.
The asphericity on the front surface may function to provide appropriate aspheric coefficients to correct for off-axis power and/or astigmatic errors.
The optical lens element accordingly may include
a spherical front surface that includes a base curvature appropriate for high base curve lenses, and
an aspheric toric back surface with appropriate aspheric coefficients to correct for off-axis power and/or astigmatism errors and a toric adjustment for astigmatic and mean power error correction to compensate for lens wrap, prescribed optical lens power and prescribed lens cylinder.
Alternatively the optical lens element includes
a toric front surface that includes a base curvature appropriate for high base curve lenses, and a toric adjustment for astigmatic and mean power error correction to compensate for lens wrap, and
an aspheric toric back surface which includes appropriate aspheric coefficients to correct for off-axis power and astigmatism errors, prescribed optical lens power and prescribed lens cylinder.
In a further alternative embodiment, the optical lens element includes
an aspheric front surface that includes a base curvature appropriate for high base curve lenses and appropriate aspheric coefficients to correct for off-axis power and/or astigmatism errors, and
an aspheric toric back surface with appropriate aspheric coefficients to correct for off axis power and/or astigmatism errors and a toric adjustment for astigmatic error correction to compensate for lens wrap, prescribed optical lens power and prescribed lens cylinder.
In a still further alternative embodiment, the optical lens element includes
an aspheric toric front surface that includes a base curvature appropriate for high base curve lenses, a toric adjustment for astigmatic error correction to compensate for lens wrap, and includes appropriate aspheric coefficients to correct for off-axis power and/or astigmatism errors, and
an aspheric toric back surface with appropriate aspheric coefficients to correct for astigmatic and mean power errors, prescribed optical lens power and prescribed lens cylinder.
In a particularly preferred embodiment, the optical lens element includes
an aspheric front surface that includes a base curvature appropriate for high base curve lenses and appropriate aspheric coefficients to define a peripheral temporal zone; and
a back surface of appropriate curvature to provide the prescribed optical lens power and prescribed lens cylinder and including adjustments for astigmatic and mean power error correction to compensate for lens wrap.
In this embodiment, the power, cylinder and error corrections may all be undertaken on the back surface, thus minimising the difficulties in designing the wrap-around type front surface.
Preferably the aspheric front surface may exhibit line symmetry about the horizontal geometric axis thereof. The aspheric front surface may alternatively or in addition exhibit line symmetry about the vertical geometric axis thereof. Such line symmetry further simplifies the design of the front lens surface whilst improving the aesthetic appearance thereof.
Preferably the aspheric surface includes a correction in the horizontal section. More preferably the back surface includes a base curvature such that patient""s required prescription power, Rx, in the prescription zone is achieved; the back surface being further modified to complement the front surface selected.
The aspheric front surface may be of generally conic shape.
In a preferred aspect of the present invention the ophthalmic lens element may be formed as a laminate of a back and front lens element.
Accordingly, in a preferred aspect of the present invention there is provided a laminate optical article adapted for mounting in a frame of the wrap-around or shield type, including
a front lens element;
a complementary back lens element, the front and back surfaces of the laminate optical article being capable of forming a prescription (Rx) zone;
the front and/or back surface bearing a correction to at least partially adjust for errors including astigmatic and mean power errors;
the front and/or back lens element optionally including
a peripheral temporal zone.
As discussed above, the laminate article may be rotated temporally about a vertical axis through the optical centre thereof, or the optical axis may be decentred relative to the geometric axis, or the lens element may be both rotated and decentred.
Accordingly, in a preferred embodiment of this aspect of the present invention there is provided a laminate optical article adapted for mounting in a frame of the wrap-around or shield type, such that the lens element is rotated temporally about a vertical axis through the optical centre thereof, including
a front lens element;
a complementary back lens element, the front and back surfaces of the laminate optical article being capable of forming a prescription (Rx) zone; the front and/or back surface bearing a correction to at least partially adjust for errors including astigmatic errors;
the front and/or back lens element optionally including
a peripheral temporal zone.
In a preferred embodiment, the front lens element may be generally plano.
The corresponding back lens element may include a lens element of positive or negative power.
If desired, there may be a distribution of distance power and cylinder between the front and back lens element.
Alternatively, the back lens element may be relatively thick, the laminate optical article forming a semi-finished lens.
In an alternative or additional aspect, the lens element may be modified to permit light control within the peripheral temporal zone. Desirably the peripheral temporal zone may be modified so that no images are created in temporal vision.
The peripheral temporal zone of the optical lens element according to the present invention may be constructed to maximise cosmetic appearance. Ideally, the peripheral temporal zone should show little or no optical difference from the remainder of the front surface of the ophthalmic lens element. For example, where the prescription Rx surface of the ophthalmic lens is a minus Rx lens, the temporal extension may exhibit a zero refractive power or positive refractive power. The temporal extension may be tapered in cross-section to maximise cosmetic acceptability.
Accordingly, in a preferred aspect the curvature of the front surface is modified in the peripheral temporal zone to substantially correspond to the curvature of the back surface thereof.
It will be understood that the peripheral temporal zone thus formed is a substantially piano extension.
The peripheral temporal zone may be treated with any suitable coatings to maximise the cosmetic appearance of the front surface thereof.
For example, the peripheral temporal zone may be designed such that there is a rapid transition from the interface between the temporal zone and the surface of refractive power such that vision will be out of focus to the wearer within the temporal extension. For example, for a minus Rx lens, the minimum degree to which the nominal power of the temporal segment should be positive relative to the distance Rx is in the range of approximately 1 to 1.25 Dioptres.
It will be understood that for a minus Rx lens, it is possible for only the front surface of the lens to bear the temporal zone. The back surface of the lens may be of conventional spherical or toric form whilst the angular reach of the temporal extension increases as the base curve of the lens is made steeper. For lenses where the base curve is relatively modest, for example 4 or 6 Dioptres, the temporal reach may be reduced compared to lenses of higher base curve. This is useful if the primary purpose of the lens design is to provide appealing cosmetics by eliminating the conventional edge on a minus Rx lens.
In an alternative aspect, where the front surface of the ophthalmic lens forms a plus Rx lens, the peripheral temporal zone may vary from the positive lens to approximately plano (for example a cylindrical lens). The ophthalmic lens of such construction may be suitable for prescriptions near piano if the temporal extension is likewise piano or slightly negative in refractive power. If the temporal extension retains some positive power as for a high plus Rx lens, this power may be at least 1 to 1.5 Dioptres less than the plus value of the Rx.
In a preferred embodiment, the front and rear surface of the optical lens element may together define a lens of minus power.
The front surface of the lens element in this embodiment may be of generally circular cross-section.
The rear surface of the lens element may be of generally conic cross-section.
The front surface to be of generally conic cross-section in the peripheral temporal zone, thus providing a generally piano temporal cross-section.
As stated above, the lens element may be modified to permit light control within the peripheral temporal zone. The reflected colour of a sunglass lens is primarily a function of the dyes at the front surface of the lens. A mirror coating may be applied to the back surface of the lens so that the combination of front and back surface reflections achieves specular intensity (mirror) and the sense of lens colour (tint). Alternatively, or in addition, a different tint coating or layer may be provided at the rear surface of the lens. This may alter both the intensity and spectral character of transmitted and reflected rays interacting with the over-tinted region of the lens.
In a further option, the front or rear surface (preferably the rear) may be frosted so that reflected and transmitted light is diffuse. That is, images are not formed by light which enters the lens. The frosted part of the lens is visually opaque (translucent) to a wearer. To someone else, the lens will reflect the tinted colour from its front surface against a dull shadow from the frosted part of the rear surface. Preferably the rear surface may include a localised mirror coating from which the reflection is a matte finish.
The peripheral temporal zone may be treated in a number of ways so that it will not create images in peripheral vision, irrespective of the optical design. The most direct methods simply prevent a perceptible intensity of focused light from passing through by blocking it with any one or a combination of:
Back Surface Gradient Mirror
Back Surface Gradient (Black) Tint
Back Surface Mist
The mirror coating may be introduced utilising conventional techniques, for example vacuum deposition of metal film on a finished lens. A chemical solution of a pristine metallic layer may be deposited on part of a casting mould and subsequently a lens is cast against that mould. A metal mirror thus formed may transmit insufficient light to form any troublesome images and reflecting a soft matte finish in copper, nickel or whatever the chosen metal.
Alternatively, or in addition, the temporal extension may include one or more of the following:
Reflection Holographic Film: mirrored polymer sheet, e.g. approximately 0.5 mm thick giving brightly coloured, changing reflected colour patterns
Light Control Film: for example polycarbonate film, e.g. 0.8 mm thick limiting light transmission to a narrow angular band
Reflective Film: for example Mylar film 0.025 mm thick, 10% transmission/90% reflection
Liquid Crystal Film: for example polymeric sheet 0.20 mm thick changing colour across the full spectrum with changing temperature.
The ophthalmic lens may be formulated from any suitable material. A polymeric material may be used. The polymeric material may be of any suitable type. The polymeric material may include a thermoplastic or thermoset material. A material of the diallyl glycol carbonate type may be used.
The polymeric article may be formed from cross-linkable polymeric casting compositions, for example as described in applicants U.S. Pat. No. 4,912,155, U.S. patent application Ser. No. 07/781,392, Australian Patent Applications 50581/93 and 50582/93, and European Patent Specification 453159A2, the entire disclosures of which are incorporated herein by reference.
Such cross-linkable polymeric casting compositions may include a diacrylate or dimethacrylate monomer (such as polyoxyalkylene glycol diacrylate or dimethacrylate or a bisphenol fluorene diacrylate or dimethacrylate) and a polymerisable comonomer, e.g. methacrylates, acrylates, vinyls, vinyl ethers, allyls, aromatic olefins, ethers, polythiols and the like.
For example, in Australian Patent Application 81216/87, the entire disclosure of which is incorporated herein by reference, applicant describes a cross-linkable coating composition including at least polyoxyalkylene glycol diacrylate or dimethacrylate and at least one poly functional unsaturated cross-linking agent.
Further, in Australian Patent Application 75160/91, the entire disclosure of which is incorporated herein by reference, applicant describes a polyoxyalkylene glycol diacrylate or dimethacrylate; a monomer including a recurring unit derived from at least one radical-polymerisable bisphenol monomer capable of forming a homopolymer having a high refractive index of more than 1.55; and a urethane monomer having 2 to 6 terminal groups selected from a group comprising acrylic and methacrylic groups.
Such polymeric formulations are UV cured or cured by a combination of UV and thermal treatment. The range of optical lenses sold under the trade designations xe2x80x9cSpectralitexe2x80x9d by Applicants have been found to be suitable.
The polymeric material may include a dye, preferably a photochromic dye, which may, for example, be added to the monomer formulation used to produce the polymeric material. The variation in depth of colour may be minimised by incorporating a pigment or dye into one or more layers of the optical article.
The ophthalmic lens element according to the present invention may further include standard additional coatings to the front or back surface including electrochromic coatings.
The front lens surface may include an anti-reflective (AR) coating, for example of the type described in U.S. Pat. No. 5,704,692 to applicants, the entire disclosure of which is incorporated herein by reference.
The front lens surface may include an abrasion resistant coating. e.g. of the type described in U.S. Pat. No. 4,954,591 to applicants, the entire disclosure of which is incorporated herein by reference.
In a particularly preferred form, the laminate ophthalmic article may include an inner layer providing desired optical properties of the type described in International Patent Application PCT/AU96/00805 to applicants, the entire disclosure of which is incorporated herein by reference.
The front and back surfaces may further include one or more additions conventionally used in casting compositions such as inhibitors, dyes including thermochromic and photochromic dyes, e.g. as described above, polarising agents, UV stabilisers and materials capable of modifying refractive index.
In a further preferred aspect of the present invention the optical lens element may be modified to accentuate facial form in the nasal region.
Accordingly the optical lens element may include a region of reduced or opposite curvature defining a nasal accentuating region.
In a more preferred form, the lens element may reach forward toward the nasal bridge and backward toward the temples.
In a still further aspect of the present invention there is provided spectacles including
a spectacle frame of the wrap-around type adapted to receive a pair of optical lenses such that each lens is rotated temporally about a vertical axis through the optical centre thereof; and
a pair of optical lens elements, each lens element including
a front and/or back surface capable of forming a prescription (Rx) surface; and optionally
a peripheral temporal zone;
the front and/or back surface bearing a surface correction to at least partially adjust for errors including astigmatic errors.
The front and back surfaces of the optical lens elements may be of the types described above. The optical lens element may be decentred.
The spectacle frame according to this aspect of the present invention may be of any suitable type. The spectacle frame may permit adjustment of the inter-pupillary distance for example via attachment of a lens to the frame supports. Frames of the rimless and temple bar type may be used.
The ophthalmic lenses mounted within the frame may be formed from a semi-finished lens or front and back lens wafer as described above. The ophthalmic lenses may bear a prescription surface of minus or plus power.
In a further aspect of the present invention, there is provided a method of designing an optical lens element adapted for mounting in a frame of the wrap-around or shield type, which method includes
providing
a mathematical or numerical representation of a surface of ;an optical lens element including a section designed to provide the desired prescription (Rx) in the prescription zone; and optionally adding thereto a mathematical or numerical representation of a peripheral temporal zone to define a complete lens surface;
rotating and/or decentring the representation of the lens surface to permit mounting in a suitable frame; and
modifying the representation of the lens surface to at least partially adjust for errors including astigmatic and mean power errors.
In a preferred aspect, the method may include
providing a mathematical or numerical representation of an aspheric front surface of an optical lens element including a section designed to provide the desired prescription (Rx) in the prescription zone and having appropriate aspheric coefficients to define a peripheral temporal zone;
rotating and/or decentring the representation of the lens surface to permit mounting in a suitable frame;
subsequently providing a mathematical or numerical representation of a prescription (Rx) back surface; and
modifying the representation of the back surface of the lens element to at least partially adjust for prismatic and/or astigmatic errors.
Preferably the method includes
providing
a mathematical or numerical representation of a surface of an optical lens element including a section designed to provide the desired prescription (Rx) in the prescription zone; and adding thereto
a first mathematical or numerical representation of a peripheral temporal zone thereto; and
a second mathematical or numerical representation of a transition section designed to smoothly blend the prescription section and peripheral temporal zone to define a complete lens surface;
rotating and/or decentring the representation of the lens surface to permit mounting in a suitable frame; and
modifying the representation of the lens surface to at least partially adjust for errors including astigmatic and mean power errors.
In a particularly preferred form the aspheric front surface is an atoric front surface. The atoric front surface may exhibit line symmetry along the horizontal and/or vertical axis.
In a further preferred form the back surface is a toric back surface.
In a preferred form the aspheric front surface may include an additional correction in the horizontal direction to adjust for errors due to rotation.
Normal representation of the cross-section of a spherical or aspheric lens surface may be via the coordinates
sag=A2R2+A4R4+A6R6+A8R8
where R is the radius measured from the optical axis and A2, A4, A6 and A8 are coefficients that define power and asphericity. It is assumed that the lens is rotationally symmetric about the optical axis.
Thus
R2=x2+z2
where the x axis is normal to the optical axis (y) in the direction towards the temples and the z axis is vertical with respect to a wearer""s face.
The use of asphericity in conventional lens design is to produce small deviations from spherical form and the components of power are defined by the surface curvatures
T=[d2y/dr2]/[1+(dy/dr)2]3/2 tangential
S=(dy/dr)/r[1+(dy/dr)2]1/2 tangential
where the sag is denoted by y.
Surface power of the lens is therefore defined by the two derivatives
dy/dr=2A2R+4A4R3+6A6R5+8A8R7,
and
d2y/dr2=2A2+12A4R2+30A6R4+56A8R8.
Torus Periphery
It is convenient to set up a torus geometry by regarding the total SAG as that due to the basic lens design curve plus a component xe2x80x9cDSAGxe2x80x9d which comes from a temporal curvature extending beyond some radius Ro and which is defined by a similar set of coefficients operating on the radial dimension (Rxe2x88x92Ro). In this case
sag=SAG Rxe2x89xa6Ro,
wherein R is the radius measured from the optical axis and A2, A4, A6 and A8 are coefficients that define power and asphericity. It is assumed that the lens is rotationally symmetric about the optical axis.
sag=SAG+DSAG Rxe2x89xa7Ro,
wherein R0 defines the periphery of the temporal region; and
DSAG=B2(Rxe2x88x92Ro)2+B4(Rxe2x88x92Ro)4+B6(Rxe2x88x92Ro)6+B8(Rxe2x88x92Ro)8
wherein B2, B4, B6 and B8 are coefficients that define power and asphericity.
The first and second derivatives of sag are then the sums of the individual derivatives
dy/drxe2x86x92dy1/dr)r=R+dy2/dr)r=Rxe2x88x92R0,
d2y/dr2xe2x86x92d2y1/dr2)r=R+d2y2/dr2)r=Rxe2x88x92R0,
where by definition both y and dy/dr are continuous at R=Ro, but the second differential is discontinuous.
In this model, then, the sagittal surface curvature is continuous and the tangential surface curvature is not unless the following condition applies
B2=0
Generalised Torus Formulation
If we generalise the expressions so that
sag=SAG+xcex1(DSAG)N for R greater than Ro,
where xcex1 and Nxe2x89xa71 are numerical parameters, we gain greater freedom to model the surface and gain better control over surface power changes at the onset of toric curvature. The first and second derivatives are continuous at R=Ro if either of the following conditions applies
2 greater than Nxe2x89xa71 and B2=O,
or
Nxe2x89xa72 for all values of B2.
Conveniently, we have found a generalised representation that provides continuity of surface curvature in both sagittal and tangential directions. That is, we can model the toric form without discontinuities in surface power. Given such forms, we are able to place one surface behind another of similar generating equation to provide a lens with strong curvatures but without discontinuities in refractive power through the lens.
When the curves produced by the above models with N=1 and N=2 are calculated and plotted, it is evident that the torus sheet blends asymptotically to the central optic zone, provided the condition on B2 is observed. The model departs very gradually from the design sphere, blending the optics of the two design zones.
Further Generalisation of Torus Formulation
It will be understood that the surfaces of a lens element are surfaces of rotation swept by any of the expressions above for sag with respect to a chosen axis of revolution. In the mathematical development above, we have specified rotational symmetry about the optical axis. This generates a lens form with the same mean surface power at horizontal and vertical meridians, having a peripheral temporal zone around the entire perimeter of the lens element.
Before such a lens element can be mounted proximate the face in a wrap around frame or shield, the temporal extension is cut away except at the locations corresponding to the temples of the wrap around eyewear.
In an alternative embodiment, the appropriate surface alteration may be formed from the SAG curves as defined above by rotating the sag curve about an axis parallel to the x axis within the plane of the horizontal meridian. The curved portions intended to provide the temporal extension of such lenses are then located towards the ends of the horizontal meridian, whilst the vertical curves may retain conventional spherical or aspheric lens form.
The expression for the sag on the surface of a lens element formed in this manner is       sag    =                            ∑                      n            =            1                    4                ⁢                              (                                                            A                                      2                    ⁢                    n                                                  ⁢                                  x                                      2                    ⁢                    n                                                              +                                                C                                      2                    ⁢                    n                                                  ⁢                                  Z                                      2                    ⁢                    n                                                                        )                    ⁢                      xe2x80x83                    ⁢          for          ⁢                      xe2x80x83                    ⁢          x                    ≤              x        0                        xe2x80x83        ⁢                                        ∑                          n              =              1                        4                    ⁢                      (                                                            A                                      2                    ⁢                    n                                                  ⁢                                  x                                      2                    ⁢                    n                                                              +                                                C                                      2                    ⁢                    n                                                  ⁢                                  Z                                      2                    ⁢                    n                                                                        )                          +                  α          ⁢                                    {                                                ∑                                      n                    =                    1                                    4                                ⁢                                  xe2x80x83                                ⁢                                                                            B                                              2                        ⁢                        n                                                              ⁡                                          (                                              x                        -                                                  x                          0                                                                    )                                                                            2                    ⁢                    n                                                              }                        N                    ⁢                      xe2x80x83                    ⁢          for          ⁢                      xe2x80x83                    ⁢          x                    ≥              x        0            
If the parameters A2n and C2n are set equal, the optic zone has the same surface power in vertical and horizontal meridians.
If the parameters C2n correspond to curves of lower power than the A2n parameters specify, the surface power of the optic zone will be lower in the vertical meridian. Lens elements formed in this way assist in achieving conformance of the wrap around eyewear to the face. A high base curve of the order of B or 9 Dioptres way be used to wrap laterally to the temples. However a lower curve, for example approximately 2 to 5 Dioptres matches the vertical shape of the face and allows the lenses to be placed closer to the eyes without indenting on the brows or cheeks.
The use of such more conventional base curves to define the vertical meridian also alleviates the need to apply off axis astigmatism and power corrections in this meridian.
The present invention will now be more fully described with reference to the accompanying figures and examples. It should be understood, however, that the description following is illustrative only and should not be taken in any way as a restriction on the generality of the invention described above.